Feedback control method and feedback control device

ABSTRACT

The response process of disturbance recovery control is divided into a follow-up phase, a convergence phase, and a stable phase. A feedback control device includes a first phase switching unit ( 3 ) which switches to the follow-up phase, a second phase switching unit ( 4 ) which switches to the convergence phase, a third phase switching unit ( 5 ) which switches to the stable phase, a first manipulated variable determining unit ( 6 ) which outputs a manipulated variable which makes the controlled variable follow up the set point in the follow-up phase, a second manipulated variable determining unit ( 7 ) which outputs a manipulated variable which makes the controlled variable converge near the set point in the convergence phase, and a third manipulated variable determining unit ( 8 ) which outputs a manipulated variable which makes the controlled variable stable at the set point in the stable phase.

BACKGROUND OF THE INVENTION

The present invention relates to a process control technique and, moreparticularly, to a feedback control method and feedback control devicewhich perform disturbance recovery control by giving a manipulatedvariable to a controlled system so as to make the controlled variablerecover to the set point at the time of application of a disturbance.

Conventionally, PID control has been known as a highly practical generalcontrol theory. As an advanced control theory like modern controltheory, for example, simple adaptive control (SAC) has been known.According to either of the control theories, a manipulated variable MVis output as a control computation result to a controlled system so asto make a controlled variable PV recover to a set point SP at the timeof application of a disturbance, and control computation is performed onthe basis of a deviation Er between the controlled variable PV and theset point SP.

General PID control is a linear control theory, and is a control theorybased on the assumption that a control system including a controlledsystem becomes a linear system. In practice, however, a controlledsystem does not have linearity in a strict sense, and PID control cantolerate slight nonlinearity. For example, heating by a halogen lamp ina RTP (Rapid Thermal Process) used in a semiconductor manufacturingapparatus is a system with strong nonlinearity to which PID controlcannot be simply applied. In this case, even PID control can be used ifonly the stability of a control system is to be pursued. However, PIDcontrol cannot cope with operation under the condition that a fasttemperature rise and a response waveform with a little overshoot arerequired as in an RTP.

Assume that the nonlinearity of a control system can be approximated bya characteristic curve K shown in FIG. 14. In this case, when thecontrolled variable PV is to be made to recover to the set point SP witha fast temperature rise (fast disturbance recovery) at the time ofapplication of a temperature-decreasing disturbance, the manipulatedvariable MV (heating output) becomes 100% at the time point when thedeviation Er between the set point SP and the controlled variable PV islarge. As a consequence, an average process gain characteristic curvehas a large gradient as indicated by “Kav1” in FIG. 14. As thetemperature rises and the deviation Er decreases, the manipulatedvariable MV decreases to, for example, about 20%. In this case, anaverage process gain characteristic curve becomes another characteristiccurve having a small gradient as indicated by “Kav2” in FIG. 14.

When the PID parameters of a PID controller are adjusted in conformitywith specifications for fast disturbance recovery, and the PIDcontroller is applied to a strong nonlinearity system like that shown inFIG. 14, a temperature rise curve (disturbance recovery waveform)becomes like a curve PV in FIG. 15. That is, in the first half period ofresponse, overshoot occurs in the controlled variable PV as in a casewherein a controlled system with an excessively large process gain iscontrolled, whereas in the second half period of response, controloperation occurs such that the controlled variable PV follows up to theset point SP at extremely low speed as in a case wherein a controlledsystem with an excessively small process gain is controlled. As aresult, a temperature rise curve like that shown in FIG. 15 appears.This control is not suitable for a controlled system for which aresponse waveform with a little overshoot is required as in the case ofa semiconductor manufacturing apparatus. In addition, adjustment of PIDparameters falls out of the range of a linear control theory, and henceis very difficult to realize.

An advanced adaptive control theory such as simple adaptive control(SAC) is designed to automatically correct the internal parameters of acontrol computation unit so as to always obtain proper controlcharacteristics with respect to variations in the process gaincharacteristic of a controlled system. However, for proper automaticcorrection (adaptive operation) for the internal parameters, controlcomputation must be performed by a sufficient number of times in atransient state. In fast disturbance recovery, the time required for atemperature rise is about 1.0 to 1.5 sec. If, therefore, the controlcycle is 50 msec, the number of times of control computation indisturbance recovery is about 20 to 30.

The number of times of control computation allowed to follow up a changein process gain due to strong nonlinearity characteristics under suchconditions is about two to three at best, as shown in FIG. 16B. Thisnumber of times of control computation is simply too small to makeadaptive operation properly function. At practical level, a techniquebased on an advanced adaptive control theory can obtain the stability ofcontrol, in the end, at best, but cannot make a controlled system withstrong nonlinearity characteristics smoothly achieve fast disturbancerecovery. This technique is substantially directed to only ensurestability in application to not only fast disturbance recovery but alsoother operations. Furthermore, there are no guidelines for practicalstandards concerning settings of many parameters to be set in advancefor proper adaptive operation.

As described above, according to the conventional PID control theory,proper disturbance recovery control cannot be realized for a controlledsystem with strong nonlinearity, and it is difficult to adjust PIDparameters.

In addition, according to an advanced adaptive control theory such assimple adaptive control (SAC), in a controlled system with strongnonlinearity characteristics, when the controlled variable is to be madeto recover to the set point at high speed, since the number of times ofcontrol computation allowed is too small to make adaptive operationproperly function, proper disturbance recovery control cannot berealized. In addition, it is difficult to adjust parameters.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems, and hasits object to provide a feedback control method and feedback controldevice which can realize proper disturbance recovery control and caneasily adjust parameters for the execution of proper disturbancerecovery control even if a system with strong nonlinearity is set as acontrolled system.

According to the present invention, there is provided a feedback controlmethod of performing disturbance recovery control by giving amanipulated variable to a controlled system so as to make a controlledvariable recover to a set point at the time of application of adisturbance, comprising the step of dividing a response process ofdisturbance recovery control into three stages including a follow-upphase, a convergence phase, and a stable phase, the first phaseswitching step of switching to the follow-up phase at a disturbanceapplication detection time point as a start time point of the follow-upphase, the follow-up phase manipulated variable determination step ofcontinuously outputting a manipulated variable which makes thecontrolled variable follow up the set point in the follow-up phase, thesecond phase switching step of switching to the convergence phase at adisturbance recovery control elapsed time point, as a start time pointof the convergence phase, at which the controlled variable does notexceed the set point in the follow-up phase, the convergence phasemanipulated variable determination step of continuously outputting amanipulated variable which makes the controlled variable converge nearthe set point in the convergence phase, the third phase switching stepof switching to the stable phase at a time point, as a start time pointof the stable phase, at which a preset state is reached in theconvergence phase, and the stable phase manipulated variabledetermination step of continuously outputting a manipulated variablewhich makes the controlled variable stable at the set point in thestable phase.

In an example of the arrangement of the feedback control methodaccording to the present invention, the first phase switching stepcomprises the step of setting a time point, as the start time point ofthe follow-up phase, at which it is confirmed on the basis of adeviation between a set point and a controlled variable that adisturbance has been applied.

In an example of the arrangement of the feedback control methodaccording to the present invention, the first phase switching stepcomprises the step of setting a time point, as the start time point ofthe follow-up phase, at which a phase switching signal is input from anexternal unit which notifies application of a disturbance.

In an example of the arrangement of the feedback control methodaccording to the present invention, the second phase switching stepcomprises the step of calculating a predicted value of a remaining timefor attainment which is a time taken for a current controlled variableto reach the set point in the follow-up phase, on the basis of adeviation between the set point and the controlled variable and acontrolled variable change ratio, and the step of setting a time point,as the start time point of the convergence phase, at which thecalculated predicted value of the remaining time for attainment becomessmaller than a preset time index.

In an example of the arrangement of the feedback control methodaccording to the present invention, the third phase switching stepcomprises the step of setting a time point, as the start time point ofthe stable phase, at which a preset time index has elapsed.

In an example of the arrangement of the feedback control methodaccording to the present invention, the follow-up phase manipulatedvariable determination step comprises the step of continuouslyoutputting a preset manipulated variable.

In an example of the arrangement of the feedback control methodaccording to the present invention, the convergence phase manipulatedvariable determination step comprises the step of continuouslyoutputting a preset manipulated variable.

In addition, according to the present invention, there is provided afeedback control device for dividing a response process of disturbancerecovery control into three stages including a follow-up phase, aconvergence phase, and a stable phase and performing disturbancerecovery control by giving a manipulated variable to a controlled systemso as to make a controlled variable recover to a set point at the timeof application of a disturbance, comprising a first phase switching unitwhich switches to the follow-up phase at a disturbance applicationdetection time point as a start time point of the follow-up phase, asecond phase switching unit which switches to the convergence phase at adisturbance recovery control elapsed time point, as a start time pointof the convergence phase, at which the controlled variable does notexceed the set point in the follow-up phase, a third phase switchingunit which switches to the stable phase at a time point, as a start timepoint of the stable phase, at which a preset state is reached in theconvergence phase, a first manipulated variable determining unit whichcontinuously outputs a manipulated variable which makes the controlledvariable follow up the set point in the follow-up phase, a secondmanipulated variable determining unit which continuously outputs amanipulated variable which makes the controlled variable converge nearthe set point in the convergence phase, and a third manipulated variabledetermining unit continuously outputs a manipulated variable which makesthe controlled variable stable at the set point in the stable phase.

In an example of the arrangement of the feedback control deviceaccording to the present invention, the first phase switching unit setsa time point, as the start time point of the follow-up phase, at whichit is confirmed on the basis of a deviation between a set point and acontrolled variable that a disturbance has been applied.

In an example of the arrangement of the feedback control deviceaccording to the present invention, the first phase switching unit setsa time point, as the start time point of the follow-up phase, at which aphase switching signal is input from an external unit which notifiesapplication of a disturbance.

In an example of the arrangement of the feedback control deviceaccording to the present invention, the second phase switching unitcalculates a predicted value of a remaining time for attainment which isa time taken for a current controlled variable to reach the set point inthe follow-up phase, on the basis of a deviation between the set pointand the controlled variable and a controlled variable change ratio, andsets a time point, as the start time point of the convergence phase, atwhich the calculated predicted value of the remaining time forattainment becomes smaller than a preset time index.

In an example of the arrangement of the feedback control deviceaccording to the present invention, the third phase switching unit setsa time point, as the start time point of the stable phase, at which apreset time index has elapsed.

In an example of the arrangement of the feedback control deviceaccording to the present invention, the manipulated variable determiningunit continuously outputs a preset manipulated variable.

In an example of the arrangement of the feedback control deviceaccording to the present invention, the second manipulated variabledetermining unit continuously outputs a preset manipulated variable.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are waveform charts for explaining a follow-up phase, aconvergence phase, and a stable phase in the present invention;

FIG. 2 is a block diagram showing the arrangement of a feedback controldevice according to the first embodiment of the present invention;

FIG. 3 is a flowchart showing the operation of the feedback controldevice in FIG. 2;

FIG. 4 is a waveform chart for explaining switching from the stablephase to the follow-up phase and switching from the follow-up phase tothe convergence phase;

FIG. 5 is a waveform chart for explaining switching from the stablephase to the follow-up phase and switching from the follow-up phase tothe convergence phase;

FIG. 6 is a waveform chart for explaining switching from the convergencephase to the stable phase;

FIG. 7 is a view for explaining a manipulated variable determinationstep in the follow-up phase;

FIG. 8 is a view for explaining a manipulated variable determinationstep in the follow-up phase;

FIGS. 9A and 9B are waveform charts showing the operation of thefeedback control device according to the first embodiment of the presentinvention;

FIG. 10 is a waveform chart for explaining a method of adjusting adeviation index in the first embodiment of the present invention;

FIG. 11 is a waveform chart for explaining a method of adjusting amanipulated variable output value from a second manipulated variabledetermining unit in the first embodiment of the present invention;

FIGS. 12A and 12B are timing charts showing the operation of a feedbackcontrol device according to the second embodiment of the presentinvention;

FIGS. 13A and 13B are timing charts showing the operation of a feedbackcontrol device according to the third embodiment of the presentinvention;

FIG. 14 is a graph showing an example of the process gain characteristicof a strong nonlinearity system;

FIG. 15 is a chart showing an example of the disturbance recoveryresponse of a strong nonlinearity system by PID control; and

FIGS. 16A and 16B are waveform charts for explaining problems in anadvanced adaptive control theory such as simple adaptive control (SAC).

DETAILED DESCRIPTION OF EMBODIMENTS First Embodiment

The first embodiment of the present invention will be described indetail below with reference to the accompanying drawings. In thisembodiment, the response process of disturbance recovery controlaccompanying the application of a disturbance is divided into threestages of phases (a follow-up phase, a convergence phase, and a stablephase). A proper, simple manipulated variable output sequence isassigned to each phase, and a series of phases are combined to forciblyand directly shape the response waveform of disturbance recoverycontrol.

FIGS. 1A and 1B are waveform charts for explaining a follow-up phase,convergence phase, and stable phase in this embodiment. FIG. 1A is achart showing changes in controlled variable PV (response waveform).FIG. 1B is a chart showing changes in manipulated variable MV. Thesymbol “◯” in FIG. 1B indicates the manipulated variable MV output ineach control cycle dt.

First of all, in a response process, the interval from a time point t1at which the application of a disturbance is detected to a specificdisturbance recovery control elapsed time point t2 at which thecontrolled variable PV does not exceed a set point SP is defined as afollow-up phase. In the follow-up phase, the response waveform ofdisturbance recovery control is not disturbed, and the manipulatedvariable MV which makes the controlled variable PV follow up the setpoint SP is continuously output.

The interval from the specific disturbance recovery control elapsed timepoint t2 to a time point t3 at which a pre-designated state is reachedis defined as a convergence phase. In the convergence phase, theresponse waveform of disturbance recovery control is not disturbed, andthe manipulated variable MV which makes the controlled variable PVconverge near the set point SP is continuously output. The time afterthe time point t3 at which the pre-designated state is reached isdefined as a stable phase. In the stable phase, the manipulated variableMV which makes the controlled variable PV stable at the set point SP iscontinuously output.

FIG. 2 is a block diagram showing the arrangement of a feedback controldevice according to this embodiment. The feedback control deviceaccording to this embodiment includes a set value input unit 1 whichinputs the set point SP set by the operator of the control device, acontrolled variable input unit 2 which inputs the controlled variable PVdetected by a sensor (not shown), a first phase switching unit 3 whichswitches to a follow-up phase at a disturbance application detectiontime point as the start time point t1 of the follow-up phase, a secondphase switching unit 4 which switches to a convergence phase at aspecific disturbance recovery control elapsed time point, at which thecontrolled variable PV does not exceed the set point SP in the follow-upphase, as the start time point t2 of the convergence phase, a thirdphase switching unit 5 which switches to a stable phase at a time pointat which a preset state is reached in the convergence phase as the starttime point t3 of the stable phase, a first manipulated variabledetermining unit 6 which continuously outputs the manipulated variableMV which makes the controlled variable PV follow up the set point SP inthe follow-up phase, a second manipulated variable determining unit 7which continuously outputs the manipulated variable MV which makes thecontrolled variable PV converge near the set point SP in the convergencephase, a third manipulated variable determining unit 8 whichcontinuously outputs the manipulated variable MV which makes thecontrolled variable PV stable at the set point SP in the stable phase,and a manipulated variable output unit 9 which outputs to a controlledsystem (not shown) the manipulated variable MV determined in accordancewith each phase.

FIG. 3 is a flowchart showing the operation of the feedback controldevice in FIG. 2. The set point SP is set by the operator of the controldevice and is input to the first phase switching unit 3, second phaseswitching unit 4, third phase switching unit 5, first manipulatedvariable determining unit 6, second manipulated variable determiningunit 7, and third manipulated variable determining unit 8 through theset value input unit 1.

The controlled variable PV for the controlled system is detected by thesensor (not shown) and is input to the first phase switching unit 3,second phase switching unit 4, third phase switching unit 5, firstmanipulated variable determining unit 6, second manipulated variabledetermining unit 7, and third manipulated variable determining unit 8through the controlled variable input unit 2.

In the initial state, a stable phase is selected. That is, at the startof control, the first phase switching unit 3 determines whether or notthe current time point is the start time point t1 of a follow-up phase(step 101 in FIG. 3). If it is determined that the current time point isnot the start time point t1, the flow advances to step 107 to maintainthe stable phase without performing phase switching. In the stablephase, the third manipulated variable determining unit 8 outputs themanipulated variable MV specified in advance, and the manipulatedvariable output unit 9 outputs the manipulated variable, output from thethird manipulated variable determining unit 8, to the controlled system(step 107).

If it is determined in step 101 that the current time point is the starttime point t1 of a follow-up phase, the first phase switching unit 3switches from the stable phase to the follow-up phase, and notifies thesecond phase switching unit 4, third phase switching unit 5, and firstmanipulated variable determining unit 6 of the switching to thefollow-up phase. In the follow-up phase, the first manipulated variabledetermining unit 6 outputs the manipulated variable MV specified inadvance, and the manipulated variable output unit 9 outputs themanipulated variable, output from the first manipulated variabledetermining unit 6, to the controlled system (step 102).

When the stable phase is switched to the follow-up phase, the secondphase switching unit 4 determines whether or not the current time pointis the start time point t2 of a convergence phase (step 103). If it isdetermined that the current time point is not the start time point t2,the flow returns to step 102 to maintain the follow-up phase withoutperforming phase switching.

If it is determined in step 103 that the current time point is the starttime point t2 of a convergence phase, the second phase switching unit 4switches from the follow-up phase to the convergence phase, and notifiesthe first phase switching unit 3, third phase switching unit 5, andsecond manipulated variable determining unit 7 of the switching to theconvergence phase. In the convergence phase, the second manipulatedvariable determining unit 7 outputs the manipulated variable MVspecified in advance, and the manipulated variable output unit 9 outputsthe manipulated variable, output from the second manipulated variabledetermining unit 7, to the controlled system (step 104).

When the follow-up phase is switched to the convergence phase, the firstphase switching unit 3 determines whether or not the current time pointis the start time point t1 of the follow-up phase (step 105). If it isdetermined that the current time point is the start time point t1 of thefollow-up phase, the flow advances to step 102 to switch from theconvergence phase to the follow-up phase, and notifies the second phaseswitching unit 4, third phase switching unit 5, and first manipulatedvariable determining unit 6 of the switching to the follow-up phase. Ifthe first phase switching unit 3 determines that the current time pointis not the start time point t1, the flow advances to step 106 tomaintain the convergence phase without performing phase switching.

The third phase switching unit 5 determines whether or not the currenttime point is the start time point t3 of a stable phase (step 106). Ifit is determined that the current time point is not the start time pointt3, the flow returns to step 104 to maintain the convergence phasewithout performing phase switching.

If it is determined in step 106 that the current time point is the starttime point t3 of the stable phase, the third phase switching unit 5switches from the convergence phase to the stable phase, and notifiesthe first phase switching unit 3, second phase switching unit 4, andthird manipulated variable determining unit 8 of the switching to thestable phase. The processing in step 107 is the same as that describedabove. The above processing in steps 101 to 107 is repeated for eachcontrol cycle dt until the control device is stopped by a command froman operator or the like (YES in step 108).

Phase switching will be described in more detail below. FIGS. 4 and 5are waveform charts for explaining switching from a stable phase to afollow-up phase and switching from a follow-up phase to a convergencephase. There are two methods of determining whether to switch from astable phase to a follow-up phase. According to one determinationmethod, the first phase switching unit 3 determines, as the follow-upphase start time point (disturbance application detection time point)t1, a time point at which a deviation Er between the set point SP andthe controlled variable PV exceeds a preset deviation index Es in astate wherein the controlled variable PV is stable near the set point SP(in the state of a stable phase), and switches from the stable phase tothe follow-up phase (FIG. 4).

According to the other determination method, the first phase switchingunit 3 determines, as the start time point t1 of a follow-up phase, atime point at which a phase switching signal is input from an externaldevice which notifies the application of a disturbance, and switchesfrom the stable phase to the follow-up phase.

There are also two methods of determining whether to switch from afollow-up phase to a convergence phase. According to one determinationmethod, the second phase switching unit 4 determines, as the convergencephase start time point (specific disturbance recovery control elapsedtime point) t2, a time point at which the deviation Er between the setpoint SP and the controlled variable PV becomes smaller than a presetdeviation index Ex, and switches from the follow-up phase to theconvergence phase (FIG. 4).

According to the other determination method, the second phase switchingunit 4 calculates a predicted value Tr of the remaining time until thecontrolled variable PV reaches the set point SP in the current controlcycle according to Tr Er/ΔPV on the basis of the deviation Er betweenthe set point SP and the controlled variable PV and a change ratio APVof the controlled variable PV. The second phase switching unit 4 thendetermines, as the convergence phase start time point (specificdisturbance recovery control elapsed time point) t2, a time point atwhich the calculated predicted value Tr of the remaining time forattainment becomes smaller than a preset time index Tx, and switchesfrom the follow-up phase to the convergence phase (FIG. 5).

FIG. 6 is a waveform chart for explaining switching from a convergencephase to a stable phase. The third phase switching unit 5 determines, asa stable phase start time point (a time point at which a pre-designatesstate is reached) t3, a time point at which a preset time index Tc haselapsed since the start time point t2 of the convergence phase, andswitches from the convergence phase to the stable phase.

A manipulated variable determination step in each phase will bedescribed next. There are three kinds of manipulated variabledetermination steps in a follow-up phase. According to the firstsequence, the first manipulated variable determining unit 6 continuouslyoutputs a preset manipulated variable MV1.

According to the second sequence, the first manipulated variabledetermining unit 6 performs time delay filter processing of the presetmanipulated variable MV1, and continuously outputs a resultant valueMVf. That is, in the second sequence, the manipulated variable MV1 isprocessed through a time delay filter like that shown in FIG. 7, and theresultant manipulated variable MVf is given to the controlled system.

According to third sequence, the first manipulated variable determiningunit 6 continuously outputs a manipulated variable MVc calculated by aPID control algorithm (including P, PD, and PI control) that attachesimportance to quick control response. That is, in the third sequence,the manipulated variable MVc is calculated by a PID control system likethat shown in FIG. 8 from the deviation Er, and is given to thecontrolled system.

In a convergence phase, the second manipulated variable determining unit7 continuously outputs a preset manipulated variable MV2. In a stablephase, the third manipulated variable determining unit 8 continuouslyoutputs a manipulated variable MVd calculated by a PID control algorithm(including P, PD, and PI control) that attaches importance to thestability of control. That is, the third manipulated variabledetermining unit 8 calculates the manipulated variable MVd from thedeviation Er by using a PID control system like that shown in FIG. 8,and gives it to the controlled system.

In this embodiment, as described above, it is an important aspect thatthe response process of disturbance recovery control is divided intothree stages of phases (a follow-up phase, a convergence phase, and astable phase). When, for example, disturbance recovery control is to beperformed for a controlled system with strong nonlinearity so as to makethe controlled variable PV recover to the set point SP at the time ofthe application of a disturbance, the average process gaincharacteristic of the controlled system in a stage corresponding to afollow-up phase greatly differs from that in a stage corresponding to astable phase.

In this case, if the follow-up phase and stable phase are to becontrolled by a control technique based on the same characteristics,control characteristics suitable for the follow-up phase are unsuitablefor the stable phase, and vice versa. For example, in fast disturbancerecovery in temperature control, since characteristics abruptly switchbetween a follow-up phase and a stable phase, the control responsewaveform is disturbed before and after the switching time point. Thatis, not only control characteristics deteriorate in either a follow-upphase or a stable phase, but also a noticeable disturbance of thecontrol response waveform appears in an intermediate stage between thetwo phases.

This embodiment is configured to perform control by the technique ofgiving different control characteristics to a follow-up phase and stablephase. In addition, a convergence phase is provided to perform controlby giving different control characteristics so as to prevent the controlresponse waveform from being disturbed before and after the switchingtime point between a follow-up phase and a stable phase.

In a follow-up phase, first of all, the manipulated variable MV aimed atonly making the controlled variable PV follow up the set point SP isoutput. In the convergence phase, the manipulated variable MV aimed atonly making the controlled variable PV converge near the set point SP isoutput to shift from the follow-up phase to the stable phase. Finally,in the stable phase, the manipulated variable MV aimed at onlystabilizing the controlled variable PV at the set point SP is output.

In this embodiment, since the control characteristics for a follow-upphase, convergence phase, and stable phase can be independentlyadjusted, parameters can be easily adjusted in accordance with an actualtarget. In disturbance recovery control, in particular, the responsewaveform of disturbance recovery control can be forcibly and directlyshaped by adjusting the switching time point between a follow-up phaseand a convergence phase and adjusting the manipulated variable MV in theconvergence phase. This makes it possible to realize smooth disturbancerecovery control.

More specific operation of this embodiment will be described next byexemplifying a case wherein the feedback control device shown in FIG. 2is applied to fast disturbance recovery control. FIGS. 9A and 9B arewaveform charts showing the operation of the feedback control deviceaccording to this embodiment. FIG. 9A is a chart showing changes incontrolled variable PV. FIG. 9B is a chart showing changes inmanipulated variable MV. As described above, the processing in steps 101to 108 in FIG. 3 is performed in each control cycle dt. The symbol “◯”in FIG. 9B indicates the manipulated variable MV output in each controlcycle dt.

In this embodiment, a switching time point (disturbance applicationdetection time point) t1 from a stable phase to a follow-up phase is atime point at which the deviation Er between the set point SP and thecontrolled variable PV exceeds the preset deviation index Es in a statewherein the controlled variable PV is stable near the set point SP (thestate of the stable phase). A switching time point (specific disturbancerecovery control elapsed time point) t2 from a follow-up phase to aconvergence phase is a time point at which the deviation Er between theset point SP and the controlled variable PV becomes smaller than thepreset deviation index Ex. A switching time point (a time point at whicha pre-designated state is reached) t3 from a convergence phase to astable phase is a time point at which the preset time index Tc haselapsed.

In this embodiment, the step of determining the manipulated variable MVin a follow-up phase is the step of continuously outputting the presetmanipulated variable MV1. The step of determining the manipulatedvariable MV in a convergence phase is the step of continuouslyoutputting the preset manipulated variable MV2. The step of determiningthe manipulated variable MV in a stable phase is the step ofcontinuously outputting the manipulated variable MVd calculated by a PIDcontrol algorithm that attaches importance to the stability of control.

In this embodiment, a parameter which indicates a phase is representedby F; F=1, F=2, and F=3 indicate a follow-up phase, convergence phase,and stable phase, respectively. Assume that a set point in a currentcontrol cycle n is represented by Sp(n); a controlled variable in thecontrol cycle n, PV(n); a manipulated variable in the control cycle n,MV(n); and a control deviation in the control cycle n, Er(n).

Assume that in step 101 or 105 in FIG. 3, the deviation Er(n) in thecurrent control cycle n is larger than the preset deviation index Es,and a deviation Er(n−1) in an immediately preceding control cycle issmaller than the deviation index Es. In this case, the first phaseswitching unit 3 sets the parameter F indicating a phase to F=1(follow-up phase), and outputs F=1 to the second phase switching unit 4,third phase switching unit 5, and first manipulated variable determiningunit 6. That is, the first phase switching unit 3 performs the followingprocessing.if Er(n)>Es and Er(n−1)<Es then F←1  (1)

Note that when receiving a notification of F=2 or F=3 from the secondphase switching unit 4 or third phase switching unit 5, the first phaseswitching unit 3 changes the value of the parameter F output to thefirst manipulated variable determining unit 6 to the notified value,i.e., F=2 or F=3.

The manipulated variable MV1 in a follow-up phase is set in advance inthe first manipulated variable determining unit 6. The first manipulatedvariable determining unit 6 outputs the preset manipulated variable MV1as the manipulated variable MV(n) when the value of the parameter Foutput from the first phase switching unit 3 is F=1 (step 102 in FIG. 3;FIG. 9B). That is, the first manipulated variable determining unit 6performs the following processing.if F=1 then MV(n)←MV 1  (2)

It suffices if the manipulated variable MV1 is set to make thecontrolled variable PV recover to the set point SP with a desiredfollow-up characteristic. When the preset invention is applied to fastdisturbance recovery control, MV1=100% is appropriate.

The second phase switching unit 4 then calculates the deviation Er(n)between the set point SP(n) and the controlled variable PV(n) in thecurrent control cycle n.Er(n)=SP(n)−PV(n)  (3)

In addition, the deviation index Ex for determination on phase switchingis set in advance in the second phase switching unit 4. Assume that instep 103 in FIG. 3, the value of the parameter F is set to F=1, the setpoint SP(n) has not changed from the set point SP(n−1), and thedeviation Er(n) is smaller than the deviation index Ex. In this case,the second phase switching unit 4 determines that the current time pointis the start time point t2 of a follow-up phase, sets the value of theparameter F to F=2 (convergence phase), and outputs F=2 to the firstphase switching unit 3, third phase switching unit 5, and secondmanipulated variable determining unit 7. That is, the second phaseswitching unit 4 performs the following processing.if F=1 and SP(n)=SP(n−1) and Er(n)<Ex then F←2  (4)

The deviation index Ex may be adjusted by trial and error to shift froma follow-up phase to a convergence phase at a proper timing, i.e., makethe controlled variable PV recover to the set point SP with a desiredfollow-up characteristic (response waveform). When the present inventionis applied to fast disturbance recovery control, an overshoot tendencyor temperature rise insufficiency tendency appears in two stages, asshown in FIG. 10. The deviation index Ex may be adjusted inconsideration of the first stage such that when overshoot occurs, thedeviation index Ex is set to a large value, whereas when temperaturerise insufficiency occurs, the deviation index Ex is set to a smallvalue. Since the deviation index Ex is a numerical value having aneffect of forcibly and directly shaping the response waveform ofdisturbance recovery control, a proper value of the deviation index Excan be easily obtained by trial and error.

Upon receiving a notification of F=1 or F=3 from the first phaseswitching unit 3 or third phase switching unit 5, the second phaseswitching unit 4 changes the value of the parameter F output to thesecond manipulated variable determining unit 7 to the notified value,i.e., F=1 or F=3.

The manipulated variable MV2 in a convergence phase is set in advance inthe second manipulated variable determining unit 7. If the value of theparameter F output from the second phase switching unit 4 is F=2, thesecond manipulated variable determining unit 7 outputs the presetmanipulated variable MV2 as the manipulated variable MV(n) (step 104 inFIG. 3; FIG. 9B). That is, the second manipulated variable determiningunit 7 performs the following processing.if F=2 then MV(n)←MV 2  (5)

The manipulated variable MV2 may be adjusted by trial and error so as tomake the controlled variable PV converge to the set point SP with adesired characteristic. When the present invention is applied to fastdisturbance recovery control, an overshoot tendency or temperature riseinsufficiency tendency appears in two stages, as shown in FIG. 11. Themanipulated variable MV2 may be adjusted in consideration of the secondstage such that when overshoot occurs, the manipulated variable MV2 isset to a small value, whereas when temperature rise insufficiencyoccurs, the manipulated variable MV2 is set to a large value. Since themanipulated variable MV2 is a numerical value having an effect offorcibly and directly shaping the response waveform of disturbancerecovery control, a proper value of the manipulated variable MV2 can beeasily obtained by trial and error.

The time index Tc for determination on phase switching is set in advancein the third phase switching unit 5. Assume that in step 106 in FIG. 3,the value of the parameter F is F=2, and an elapsed time tn from thetime point t2 set in F=2 (convergence phase) is longer than the timeindex Tc. In this case, the third phase switching unit 5 determines thatthe current time point is the start time point t3 of a stable phase,sets the value of the parameter F to F=3 (stable phase), and outputs F=3to the first phase switching unit 3, second phase switching unit 4, andthird manipulated variable determining unit 8. That is, the third phaseswitching unit 5 performs the following processing.if F=2 and tn>Tc then F←3  (6)

The time index Tc may be adjusted by trial and error so as to make thecontrolled variable PV converge to the set point SP with a desiredcharacteristic. When the present invention is applied to fastdisturbance recovery control, it is appropriate to set this index to atime about one to two times a process wasteful time Lp for thecontrolled system. Note that upon receiving a notification of F=1 or F=2from the first phase switching unit 3 or second phase switching unit 4,the third phase switching unit 5 changes the value of the parameter Foutput to the third manipulated variable determining unit 8 to thenotified value, i.e., F=1 or F=2.

If the value of the parameter F output from the third phase switchingunit 5 is F=3, the third manipulated variable determining unit 8 outputsas the manipulated variable MV(n) a manipulated variable MVd(n)calculated by a PID control algorithm that attaches importance to thestability of control (step 107 in FIG. 3; FIG. 9B). That is, the thirdmanipulated variable determining unit 8 performs the followingprocessing.

-   -   if F=3 then MV(n)←MVd(n)  (7)

In this case, the PID control algorithm that attaches importance to thestability of control is expressed by a transfer function using Laplaceoperators as follows:MVd(n)=Kg 3{1+(1/Ti 3 s)+Td 3 s)}{SP(n)−PV(n)}  (8)

In equation (8), Kg3 is a proportional gain, Ti3 is an integral time,and Td3 is a derivative time. Note that the manner of setting theparameters Kg3, Ti3, and Td3 for the attachment of importance tostability is known, and hence a description thereof will be omitted.

As described above, according to this embodiment, the response processof disturbance recovery control is divided into three stages, namely afollow-up phase, convergence phase, and stable phase, and the respectivephases are switched such that a disturbance application detection timepoint is regarded as the start time point of a follow-up phase, aspecific disturbance recovery control elapsed time point at which thecontrolled variable does not exceed the set point in the follow-up phaseis regarded as the start time point of a convergence phase, and a timepoint at which a preset state is reached in the convergence phase isregarded as the start time point of a stable phase. In the follow-upphase, a manipulated variable which makes the controlled variable followup the set point is output. In the convergence phase, a manipulatedvariable which makes the controlled variable converge near the set pointis output. In the stable phase, a manipulated variable which makes thecontrolled variable stable at the set point is output. Since the controlcharacteristics for a follow-up phase, convergence phase, and stablephase can be adjusted independently, parameters can be easily adjustedin accordance with an actual target. The response waveform ofdisturbance recovery control can be forcibly and directly shaped byadjusting the switching time point from a follow-up phase to aconvergence phase and adjusting the manipulated variable in theconvergence phase, in particular. Even if, therefore, a system withstrong nonlinearity is a controlled system, appropriate disturbancerecovery control can be realized. In addition, in this embodiment, evenif the number of times of control computation is insufficient accordingto an advanced adaptive control theory such as simple adaptive control(SAC), appropriate control can be realized even in the case of, forexample, fast disturbance recovery control.

Second Embodiment

The second embodiment of the present invention will be described next.This embodiment shows another example in which the present invention isapplied to fast disturbance recovery control. In this embodiment, thearrangement of a feedback control device and the flow of processing arethe same as those shown in FIGS. 2 and 3, and hence will be described byusing reference numerals in FIGS. 2 and 3. FIGS. 12A and 12B arewaveform charts showing the operation of the feedback control deviceaccording to this embodiment. FIG. 12A is a chart showing changes incontrolled variable PV. FIG. 12B is a chart showing changes inmanipulated variable MV. The symbol “◯” in FIG. 12B indicates themanipulated variable MV output in each control cycle dt.

In this embodiment, assume that a switching time point (disturbanceapplication detection time point) t1 from a stable phase to a follow-upphase is a time point at which a deviation Er between a set point SP anda controlled variable PV becomes larger than a preset deviation index Esin a state wherein the controlled variable PV is stable near the setpoint SP (the state of a stable phase).

Assume also that a switching time point (specific disturbance recoverycontrol elapsed time point) t2 from a follow-up phase to a convergencephase is a time point at which a predicted value Tr=Er/ΔPV of theremaining time for attainment calculated on the basis of the deviationEr between the set point SP and the controlled variable PV and a changeratio ΔPV of the controlled variable PV becomes smaller than a presettime index Tx. Assume further that a switching time point (a time pointat which a pre-designated state is reached) t3 from a convergence phaseto a stable phase is a time point at which a preset time index Tc haselapsed.

In this embodiment, the step of determining the manipulated variable MVin a follow-up phase is the step of processing a preset manipulatedvariable MV1 through a time delay filter and continuously outputting aresultant value MVf. The step of determining the manipulated variable MVin a convergence phase is the step of continuously outputting a presetmanipulated variable MV2. The step of determining the manipulatedvariable MV in a stable phase is the step of continuously outputting amanipulated variable MVd calculated by a PID control algorithm thatattaches importance to the stability of control.

The operation of a first phase switching unit 3 is the same as that inthe first embodiment. The manipulated variable MV1 and a primary delayfilter time constant Tf in a follow-up phase are set in advance in afirst manipulated variable determining unit 6. If the value of aparameter F output from the first phase switching unit 3 is F=1, thefirst manipulated variable determining unit 6 processes the preset valueMV1 through a primary delay filter, and outputs a resultant value MVf(n)as manipulated variable MV(n) (step 102 in FIG. 3; FIG. 12B). That is,the first manipulated variable determining unit 6 performs the followingprocessing.if F=1 then MV(n)←MVf(n)  (9)

In this case, an arithmetic expression of primary delay filterprocessing is expressed by a transfer function using Laplace operatorsas follows:MVf(n)={1/(1+Tfs)}MV 1  (10)

The first manipulated variable determining unit 6 calculates the valueMVf after primary delay filter processing according to expression (9).

The manipulated variable MV1 may be set to make the controlled variablePV follow up the set point SP with a desired follow-up characteristic.When the present invention is applied to fast disturbance recoverycontrol, MV1=100% is appropriate. The primary delay filter time constantTf may be arbitrarily set such that the disturbance recovery speed atwhich the controlled variable PV recovers to the set point SP after theapplication of a disturbance is set to a desired speed. When the presentinvention is applied to fast disturbance recovery control, an adjustmentcan be made to decrease the temperature rise rate by increasing theprimary delay filter time constant Tf.

A second phase switching unit 4 then calculates a deviation Er(n)between a set point SP(n) and a controlled variable PV(n) in a currentcontrol cycle n according to equation (3). The second phase switchingunit 4 also calculates a predicted value Tr(n) of the remaining timeuntil the controlled variable PV reaches the set point SP in the currentcontrol cycle as follows: $\begin{matrix}\begin{matrix}{{{Tr}(n)} = {{{{Er}(n)}/\Delta}\quad{PV}}} \\{= {{{Er}(n)}{{dt}/\{ {{{Pv}(n)} - {{PV}( {n - 1} )}} \}}}}\end{matrix} & (11)\end{matrix}$

In equation (11), dt is a control cycle, and PV(n−1) is a controlledvariable in an immediately preceding control cycle.

The time index Tx for determination on phase switching is set in advancein the second phase switching unit 4. Assume that in step 103 in FIG. 3,the value of the parameter F is F=1, the set point SP(n) has not changedfrom a set point SP(n−1), and a predicted value Tr(n) of the remainingtime for attainment is smaller than the time index Tx. In this case, thesecond phase switching unit 4 sets the value of the parameter F to F=2(convergence phase), and outputs F=2 to the first phase switching unit3, a third phase switching unit 5, and a second manipulated variabledetermining unit 7. That is, the second phase switching unit 4 performsthe following processing.if F=1 and SP(n)=SP(n−1) and Tr(n)<Tx then F←2  (12)

The time index Tx may be adjusted by trail and error to shift from afollow-up phase to a convergence phase at a proper timing, i.e., makethe controlled variable PV recover to the set point SP with a desiredfollow-up characteristic. When the present invention is applied to fastdisturbance recovery control, an overshoot tendency or temperature riseinsufficiency tendency appears in two stages, as shown in FIG. 10. Thetime index Tx may be adjusted in consideration of the first stage suchthat when overshoot occurs, the time index Tx is corrected into a largevalue, whereas when temperature rise insufficiency occurs, the timeindex Tx is corrected into a small value. Since the time index Tx is anumerical value having an effect of forcibly and directly shaping theresponse waveform of disturbance recovery control, a proper value of thetime index Tx can be easily obtained by trial and error.

The operations of second manipulated variable determining unit 7, thirdphase switching unit 5, and third manipulated variable determining unit8 are the same as those in the first embodiment.

Third Embodiment

The third embodiment of the present invention will be described next.This embodiment shows another example in which the present invention isapplied to fast disturbance recovery control. In this embodiment, thearrangement of a feedback control device and the flow of processing arethe same as those shown in FIGS. 2 and 3, and hence will be described byusing reference numerals in FIGS. 2 and 3. FIGS. 13A and 13B arewaveform charts showing the operation of a feedback control deviceaccording to this embodiment. FIG. 13A is a chart showing changes incontrolled variable PV. FIG. 13B is a chart showing changes inmanipulated variable MV. The symbol “◯” in FIG. 13B indicates themanipulated variable MV output in each control cycle dt.

In this embodiment, assume that a switching time point (disturbanceapplication detection time point) t1 from a stable phase to a follow-upphase is a time point at which a phase switching signal is input from anexternal device which notifies the application of a disturbance. In thefield of process control, the application of a disturbance can sometimesbe detected before the controlled variable PV actually changes. Before achange in controlled variable PV appears, therefore, a phase switchingsignal can also be input in a feedforward manner.

Assume that a switching time point (specific disturbance recoverycontrol elapsed time point) t2 from a follow-up phase to a convergencephase is a time point at which a predicted value Tr=Er/ΔPV of theremaining time for attainment calculated on the basis of a deviation Erbetween a set point SP and the controlled variable PV and a change ratioAPV of the controlled variable PV becomes smaller than a preset timeindex Tx. Assume further that a switching time point (a time point atwhich a pre-designated state is reached) t3 from a convergence phase toa stable phase is a time point at which a preset time index Tc haselapsed.

In this embodiment, the step of determining the manipulated variable MVin a follow-up phase is the step of continuously outputting amanipulated variable MVc calculated by a PID control (including P, PD,and PI control) algorithm that attaches importance to quick controlresponse. Assume also that the step of determining the manipulatedvariable MV in a convergence phase is the step of continuouslyoutputting a preset manipulated variable MV2, and the step ofdetermining the manipulated variable MV in a stable phase is the step ofcontinuously outputting a manipulated variable MVd calculated by a PIDcontrol algorithm that attaches importance to the stability of control.

When a phase switching signal Sf is externally input in step 101 or 105in FIG. 3, a first phase switching unit 3 determines that the currenttime point is the start time point t1 of a follow-up phase, sets thevalue of a parameter F indicating a phase to F=1 (follow-up phase), andoutputs F=1 to a second phase switching unit 4, third phase switchingunit 5, and first manipulated variable determining unit 6. That is, thefirst phase switching unit 3 performs the following processing.if Sf is input then F←1   (13)

If the value of the parameter F output from the first phase switchingunit 3 is F=1, the first manipulated variable determining unit 6 outputsa manipulated variable MVc(n) calculated by a PID control algorithm thatattaches importance to quick control response as manipulated variableMV(n) (step 102 in FIG. 3; FIG. 13B). That is, the first manipulatedvariable determining unit 6 performs the following processing.if F=1 then MV(n)←MVc(n)  (14)

In this case, the PID control algorithm that attaches importance to thestability of control is expressed by a transfer function using Laplaceoperators as follows:MVc(n)=Kg 1(1+(1/Ti 1 s)+Td 1 s)(SP(n)−PV(n))  (15)

In equation (15), Kg1 is a proportional gain, Ti1 is an integral time,and Td1 is a derivative time. Note that the manner of setting theparameters Kg1, Ti1, and Td1 for the attachment of importance to quickresponse is known, and hence a description thereof will be omitted.

The operation of the second phase switching unit 4 is the same as thatin the second embodiment. The operations of a second manipulatedvariable determining unit 7, the third phase switching unit 5, and athird manipulated variable determining unit 8 are the same as those inthe first embodiment.

Obviously, the present invention is not limited to each embodimentdescribed above, and each embodiment can be changed as needed within thetechnical category of the invention. For example, as described above inthe first embodiment, there are two methods of determining whether ornot to switch from a stable phase to a convergence phase, there are twomethods of determining whether or not to switch from a follow-up phaseto a convergence phase, there is one method of determining whether ornot to switch from a convergence phase to a stable phase, there arethree steps of determining a manipulated variable for a follow-up phase,there is one step of determining a manipulated variable for aconvergence phase, and there is one step of determining a manipulatedvariable for a stable phase. Therefore, the maximum number ofcombinations of the respective determination methods and the respectivemanipulated variable determination steps is 2×2×1×3×1×1, i.e., 12, andany one of the combinations can be used.

According to the third sequence (the third embodiment) of themanipulated variable determination steps in a follow-up phase, the firstmanipulated variable determining unit 6 continuously outputs themanipulated variable MVc calculated by the PID control algorithm thatattaches importance to quick response control. However, the presentinvention is not limited to this. For example, control with importancebeing attached to quick response by using another control algorithm suchas IMC (Internal Model Control) may be performed.

Likewise, in a stable phase, the third manipulated variable determiningunit 8 continuously outputs the manipulated variable MVd calculated bythe PID control algorithm with importance being attached to thestability of control. However, the present invention is not limited tothis, and control with importance being attached to stability may beperformed by using another control algorithm.

Industrial Applicability

As has been described above, the feedback control method and feedbackcontrol device according to the present invention are suitable forprocess control, and more particularly, for process control aimed at asystem with strong nonlinearity as a controlled system.

1. A feedback control method of performing disturbance recovery controlby giving a manipulated variable to a controlled system so as to make acontrolled variable recover to a set point at the time of application ofa disturbance, comprising: dividing a response process of disturbancerecovery control into three stages including a follow-up phase, aconvergence phase, and a stable phase; a first phase switching step ofswitching to the follow-up phase at a disturbance application detectiontime point as a start time point of the follow-up phase; the follow-upphase manipulated variable determination step of continuously outputtinga manipulated variable which makes the controlled variable follow up theset point in the follow-up phase; the second phase switching step ofswitching to the convergence phase at a disturbance recovery controlelapsed time point, as a start time point of the convergence phase, atwhich the controlled variable does not exceed the set point in thefollow-up phase; the convergence phase manipulated variabledetermination step of continuously outputting a manipulated variablewhich makes the controlled variable converge near the set point in theconvergence phase so as to prevent a control response waveform frombeing disturbed before and after a switching time point between thefollow-up phase and the stable phase; the third phase switching step ofswitching to the stable phase at a time point, as a start time point ofthe stable phase, at which a preset state is reached in the convergencephase; and the stable phase manipulated variable determination step ofcontinuously outputting a manipulated variable which makes thecontrolled variable stable at the set point in the stable phase.
 2. Afeedback control method according to claim 1, characterized in that thefirst phase switching step comprises the step of setting a time point,as the start time point of the follow-up phase, at which it is confirmedon the basis of a deviation between a set point and a controlledvariable that a disturbance has been applied.
 3. A feedback controlmethod according to claim 1, characterized in that the first phaseswitching step comprises the step of setting a time point, as the starttime point of the follow-up phase, at which a phase switching signal isinput from an external unit which notifies application of a disturbance.4. A feedback control method according to claim 1, characterized in thatthe second phase switching step comprises the step of calculating apredicted value of a remaining time for attainment which is a time takenfor a current controlled variable to reach the set point in thefollow-up phase, on the basis of a deviation between the set point andthe controlled variable and a controlled variable change ratio, and thestep of setting a time point, as the start time point of the convergencephase, at which the calculated predicted value of the remaining time forattainment becomes smaller than a preset time index.
 5. A feedbackcontrol method according to claim 1, characterized in that the thirdphase switching step comprises the step of setting a time point, as thestart time point of the stable phase, at which a preset time index haselapsed.
 6. A feedback control method according to claim 1,characterized in that the follow-up phase manipulated variabledetermination step comprises the step of continuously outputting apreset manipulated variable.
 7. A feedback control method according toclaim 1, characterized in that the convergence phase manipulatedvariable determination step comprises the step of continuouslyoutputting a preset manipulated variable.
 8. A feedback control devicefor dividing a response process of disturbance recovery control intothree stages including a follow-up phase, a convergence phase, and astable phase and performing disturbance recovery control by giving amanipulated variable to a controlled system so as to make a controlledvariable recover to a set point at the time of application of adisturbance, comprising: a first phase switching unit which switches tothe follow-up phase at a disturbance application detection time point asa start time point of the follow-up phase; a second phase switching unitwhich switches to the convergence phase at a disturbance recoverycontrol elapsed time point, as a start time point of the convergencephase, at which the controlled variable does not exceed the set point inthe follow-up phase; a third phase switching unit which switches to thestable phase at a time point, as a start time point of the stable phase,at which a preset state is reached in the convergence phase; a firstmanipulated variable determining unit which continuously outputs amanipulated variable which makes the controlled variable follow up theset point in the follow-up phase; a second manipulated variabledetermining unit which continuously outputs a manipulated variable whichmakes the controlled variable converge near the set point in theconvergence phase so as to prevent a control response waveform frombeing disturbed before and after a switching time point between thefollow-up phase and the stable phase; and a third manipulated variabledetermining unit continuously outputs a manipulated variable which makesthe controlled variable stable at the set point in the stable phase. 9.A feedback control device according to claim 8, characterized in thatsaid first phase switching unit sets a time point, as the start timepoint of the follow-up phase, at which it is confirmed on the basis of adeviation between a set point and a controlled variable that adisturbance has been applied.
 10. A feedback control device according toclaim 8, characterized in that said first phase switching unit sets atime point, as the start time point of the follow-up phase, at which aphase switching signal is input from an external unit which notifiesapplication of a disturbance.
 11. A feedback control device according toclaim 8, characterized in that said second phase switching unitcalculates a predicted value of a remaining time for attainment which isa time taken for a current controlled variable to reach the set point inthe follow-up phase, on the basis of a deviation between the set pointand the controlled variable and a controlled variable change ratio, andsets a time point, as the start time point of the convergence phase, atwhich the calculated predicted value of the remaining time forattainment becomes smaller than a preset time index.
 12. A feedbackcontrol device according to claim 8, characterized in that said thirdphase switching unit sets a time point, as the start time point of thestable phase, at which a preset time index has elapsed.
 13. A feedbackcontrol device according to claim 8, characterized in that saidmanipulated variable determining unit continuously outputs a presetmanipulated variable.
 14. A feedback control device according to claim8, characterized in that said second manipulated variable determiningunit continuously outputs a preset manipulated variable.